we couldn't bring up the OSPF3 connectivity between MX and QFX and its giving the license error and not even listing out the OSPF3 interfaces.

"show ospf3 interfaces" wont display any OSPF3 neighbor but OSPFv2 will come up fine

Customer has not configured "family inet6" configuraton and without that OSPF3 will not be able to establish the v6 sessions through link-local addresses if no manual IPv6 address configured, so it will not be able to host the realm ipv4 sessions on top of ipv6 based OSPF3 session.

MW completed successfully post adding "family inet6" configurations for OSPF3 neighbors.